This invention relates to polymers and polyblends, comprising, as polymerized components, an unsaturated dicarboxylic acid anhydride. More specifically, it relates to such polymers and polyblends that have been stabilized against certain effects of high temperatures.
It has been found that polymers containing polymerized maleic anhydride have a tendency to decompose at elevated temperatures. It is believed that this occurs by a rupture of the polymer chain at a maleic anhydride segment with consequent evolution of carbon dioxide. In a molded item this can result in unsightly splaying and blistering of the surface of the molded item. The effect increases with the anhydride content.
It has further been found that when maleic anhydride and acylonitrile are present in the same polymeric environment, there is an apparent tendency for a reaction to occur that results in crosslinking and sometimes the evolution of carbon dioxide and/or water. This reaction occurs at elevated temperatures of the kind that can be reached during extrusion and molding operations. It would appear that the crosslinking occurs whether the acrylonitrile and maleic anhydride components are in the same or different polymer molecules.
The effect increases in significance with the amounts of the components and generally above about 15% of each component in a polymer composition is enough to generate the effect to a noticeable extent if the temperature is sufficiently elevated, that is above about 265.degree. C.
While it is usually possible to extrude and mold at lower temperatures where no problem is encountered, it is desirable to provide accommodation for the wide variation of conditions that occur as a matter of course in a commerical operation. The present invention provides a means of reducing the significance of the crosslinking effect thus permitting the use of a wider range of molding and extrusion conditions with such polymers.